MELBOURNE, Australia - Unseeded American CoCo Vandeweghe looks to back up her win over the WTA World No.1 Angelique Kerber with another big upset, this time against No.7 seed Garbiñe Muguruza. Venus Williams hopes to stay on course to another all-Williams final, but a tricky opponent stands in her way. Who will grab the first two spots into the semifinals?
We preview all the Day 9 matchups right here on wtatennis.com.
CoCo Vandeweghe (USA #35) vs  Garbiñe Muguruza (ESP #7)
Head-to-head: Vandeweghe leads 2-1
Key Stat: Vandeweghe is the first American (other than Serena Williams and Venus Williams) to defeat a WTA World No.1 since Jennifer Capriati defeated Martina Hingis at 2001 French Open
The battle-tested Vandeweghe also comes into her quarterfinal matchup with an extra bit of confidence, having already defeated her next opponent Garbiñe Muguruza two times previously.
But both of those wins came on grass - Vandeweghe's favored surface - and both came back in 2014, before the Spaniard rocketed up the rankings and claimed her maiden Grand Slam title.
"It's an interesting matchup because [Muguruza] holds a different aspect to a playing style of she's an aggressor, as well.She is going to play that way, and no other way," Vandeweghe assessed after her win over Kerber.
"For me it depends on if I can match it, as well as if I can beat her to that punch of getting first strike, first play."
Muguruza struggled with form earlier in the season, but in Melbourne she looks locked in. After overcoming her usual slow starts, Muguruza has rediscovered her lethal aggression, winning matches more decisively and as a result, hasn't dropped a set all tournament long.
 Venus Williams (USA #17) vs  Anastasia Pavlyuchenkova (RUS #27)
Head-to-head: Venus leads 3-2
Key Stat: 2017 Australian Open marks Venus' 73rd Grand Slam main draw appearance - the Open Era record
The oldest woman in the draw is turning back the years as Venus Williams is back into the Australian Open quarterfinals for the ninth time. And on the other side of the draw sits Serena Williams, with the sisters looking on course for yet another all-Williams final.
But let's not get too ahead of ourselves, because standing between Venus and a semifinal berth is No.24 seed Anastasia Pavlyuchenkova. Venus leads the pair's head-to-head 3-2, with Pavlyuchenkova's last victory coming in 2009.
But the veteran former No.1 understands that, at this stage of the tournament, everyone is a threat - especially the younger players.
"Today I played a qualifier, and she hardly ever missed. So it doesn't matter who you come up against, they are coming and they want to win, too," Venus told press after her win against Mona Barthel.
"They have nothing to lose. I'm going to be focused on winning one round at a time and focus on doing what it takes to be there."
Around the Grounds?
The doubles tournament is heating up as the top seeded Frenchwomen Caroline Garcia and Kristina Mladenovic are back in action in the quarterfinals, eying their first Australian Open title - and the doubles No.1 ranking. But they're up against their biggest test of the tournament as they take to Rod Laver Area against the all-Aussie duo of Ashleigh Barty and Casey Dellacqua. The Australians harnessed all the home support in their second-round upset of No.5 seeds Martina Hingis and CoCo Vandeweghe, and will look to strike again on the tournament's biggest stage.
Also in action, No.2 seeds Bethanie Mattek-Sands and Lucie Safarova take on No.11 seeds Raquel Atawo and Xu Yifan, and No.3 seeded Russians Ekaterina Makarova and Elena Vesnina square up against No.12 seeds Andrea Hlavackova and Peng Shuai.